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          Odhner Pinwheel Calculator

    This is a wonderful machine, and I'd been exposed to its wonders as a small child, the age when wonders are best appreciated. My father borrowed one of these from the university to do his Physics research. He’d work late into the night, to the sound of whirring gears and a ringing bell (the bell indicated a result going negative, though I couldn't know this at the time). And when he was out, I'd have a wonderful time cranking the handles and observing the mystifying action. The calculator tolerated all this -- in those days machines were built to stand abuse, not to fear it.
    Later, when I was a student in the mid-70's, there were still such machines in use at the Physics department; but they were gone by the time I'd graduated, casualties of the far more effective electronic calculators. Later still, when eBay made it possible to find anything whatsoever, I made an effort to find the exact same model my father had used, and I had it shipped over from Europe, to take a proud place in my collection. Odhner calculator
Click photo to enlarge
    W.T. Odhner invented his very successful “pinwheel” four-function calculator mechanism in Russia in 1874, and his invention was cloned by numerous companies, resulting in dozens of similar models that remained in wide use for almost a century. The machine on display here was made by the Odhner firm in Sweden around 1940. It is heavy with mechanical subtleties: just press a key, to advance the carriage with a well-oiled, assertive thump-clunk, and you get a feeling of being in the presence of a piece of quality engineering.
    Numbers are dialed into the sliding levers on the top part of the machine, and are added to the register visible in the carriage at the bottom when the large crank is turned. Shifting the carriage sideways allows multiplication through a sequence of addition operations; the two small cranks zero the registers. The design includes ingenious error-preventing interlocks between all the controls: should the operator fail to return a crank to its resting position, the other controls are frozen until this is corrected.
    When I received this machine in the mail, I invited my parents to see it, without telling them what they are going to see. They recognized it instantly, of course -- and my mother's first question was "does it still ring a bell?"
    Yes, indeed, it sure does.

Exhibit provenance:
    I bought this machine on eBay from a German merchant specializing in antique technology.

More info:
    - History of Odhner calculators: .
    - Detailed description of an Odhner's complex mechanism on John Wolff's site.
    - And see this article for a comparison with the Soviet "Iron Felix" calculator.

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